This application claims the priority of German patent document 199 44 185.5, filed 15 Sep. 1999, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an apparatus for carrying out a heterogeneously catalyzed reaction by supplying a suitable reaction mixture to a catalyst, as well as to a method for producing the apparatus.
An example of heterogeneously catalyzed reactions is the production of hydrogen from a hydrocarbon or alcohol, especially from methanol (i.e., methanol reforming). A reaction mixture comprising a hydrocarbon or alcohol and water is supplied to a catalyst. Further examples are the carbon monoxide depletion with release of carbon dioxide in a so-called hydrogen shift reaction; the oxidation of carbon monoxide by supplying a gas-containing carbon monoxide and a gas-containing oxygen to a catalyst; as well as the combustion of a combustible educt with addition of an oxygen-containing gas in a catalytic burner.
The recovery of hydrogen from methanol is based on the overall reaction
CH3OH+H2O----- greater than CO2+3H2 
For carrying out this reaction, a reaction mixture comprising a hydrocarbon and water vapor is passed along a suitable catalyst. Heat is supplied at the same time in order to produce the desired hydrogen in a 2-step or multi-step reaction. Such an apparatus for two-step methanol reforming is known from EP 0 687 648 A1. In the known apparatus, the reaction mixture is supplied to a first reactor, in which a partial conversion of the methanol occurs. After passing through the first reactor, the gas mixture, in which portions of still unreacted educt are contained, is passed into a second reactor, which is optimized for the reaction. The reactors are constructed as plate reactors or bulk reactors, in which the catalyst is provided in the form of a fill or a coating on the distributing channels. Moreover, catalysts are known in the form of coated sheet metal, nets and foams, through which the reaction mixture flows.
From EP 0 217 532 B1, a method is known for the catalytic production of hydrogen from mixtures of methanol and oxygen using a gas-permeable catalyst system, for which a hydrogen generator is provided with an upper reaction zone and a lower reaction zone. The reaction mixture of methanol and oxygen is supplied to the upper reaction zone. After flowing through the upper reaction zone, the reaction mixture is passed into the lower reaction zone, in which, due to a spontaneous initiation of the oxidation of the methanol, there is such an increase in temperature, that a partial oxidation of the methanol commences in the upper reaction zone in the presence of a copper catalyst and hydrogen is formed.
EP 0 906 890 A1 discloses an apparatus for carrying out a heterogeneously catalyzed reaction in which a suitable reaction mixture is supplied to a catalyst, which is prepared by compressing a catalyst powder into a highly compressed layer forming a molded object. The reaction mixture can be forced through the catalyst layer with a drop in pressure. In order to seal them from the surroundings, such reactors usually have a massive metal housing.
It is an object of the present invention to provide an apparatus, which is an improvement with respect to weight and costs. Furthermore, it is an object of the present invention to provide a method for manufacturing such an apparatus.
This objective is accomplished by an apparatus and by a method according to the present invention.
The integration of a seal directly on or in the edge region of a stack of pressed layers represents a solution, which is an improvement with respect to weight and costs, since previously sealing of the edges was realized usually with a massive metallic housing. In contrast, pursuant to the present invention, a stack is sealed (1) in a stacking direction by end plates, and (2) transversely to the stacking direction by an integrated edge seal.
To increase safety, a sheet can be provided that surrounds the stack gas-tight. The escape of combustion gases through small leaks in the edge seal into the surroundings is avoided. For venting purposes, one or more openings provided with a catalyst can be provided. Accordingly, emerging combustion gases are reacted completely with the oxygen of the surrounding air, so that contamination of the environment is reduced.
In an advantageous development of the present invention, the catalyst material is pressed together with a supporting structure, as a result of which the catalyst material is stabilized mechanically and/or the thermal conductivity is improved. The carrier structure advantageously is a three-dimensional network structure (i.e., matrix) which, in a further advantageous development of the present invention, is a metallic supporting structure. Copper, especially dendritic copper, for example, is used as the metal.
For the preparation of the edge seal by an increased consolidation of the catalyst material in an edge region, it is only necessary to adapt the pressing tools and molds correspondingly. The tightness can be improved by admixing additional materials in the edge region, since these materials can be selected especially with regard to their sealing function. Although a subsequent sintering step can represent an increased expense for the manufacture, this method of manufacturing is used preferably in cases in which the catalyst material is also subjected to a sintering step, so that no additional effort is required.
In relation to quality control, the selection of a material that forms an edge seal under processing conditions is disadvantageous, since the tightness is brought about only after the equipment is started up. On the other hand, however, an additional manufacturing step can be omitted as a result.
A plurality of proven methods is available for applying a material, which is impermeable to gases and temperature resistant, on the finished stack of layers. The use of a soldering foil for sealing the edge has had very good results with respect to tightness.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.